Filtration of blood has been utilized in the past with cardio-pulmonary bypass techniques to remove contaminants from the blood that may in some way alter the blood, which may eventually result in damage to the perfused tissue. It has been shown that some of these problems are due to the blood oxygenators that produce microemboli which is a result of the proportion at which the oxygen and the blood were mixed.
To remove the microemboli, disposable filters have been utilized. Examples of these are those described in U.S. Pat. Nos. 3,701,433 and 3,696,932, both issued to Pall Corporation. In these types of disposable filters, oxygenated blood enters a first chamber which has a cylindrical filter disposed therein. The interior of the cylindrical filter is sealed off from the first and outer chamber and then a conduit interfaced with the interior of the filter for allowing blood to exit. The filter filters out the gas and microemboli, which gas is then purged from a vent or from a self-venting device. Therefore, surges, entrained microbubbles or inadvertent air boluses can be removed even at high flow rates.
One disadvantage to previous disposable filters is the pore size on the filters and the maximum flow rate therethrough. If the flow rate is increased, the filter will still filter out the undesired contaminants and air microbubbles, but damage may occur to the blood. Therefore, a given filter has an intrinsic maximum available flow rate. In order to increase flow rates, it is necessary to increase the pore size which can have a deleterious effect in that it may not filter out all particles. Therefore, there exists a need for a disposable filter that will maintain the filtration level while allowing an increased flow rate without altering the blood.